The high density packaging of electronic components frequently involves the wave soldering of printed circuit board assemblies. In the wave solder operation the electrical interconnections of the components are accomplished en masse as the underside of the circuit board is transported through the solder bath in a semi-automatic operation. The circuit itself, together with the components mounted thereon, represent a costly investment. Yet problems have existed for some time in the soldering operation which may render the circuit board completely unusable, or at best, usuable after considerable rework. The latter is accomplished only at substantial labor cost and delay. These problems include damage to the circuit board edge connectors which are usually gold plated. The damage may be the result of unwanted solder coating or the scratching or abrading of the gold surface by the masking means used to prevent the former occurrence. Other problems involve the warping or sagging of the circuit boards as they are subjected to the high heat of the molten solder, and the overflow of the solder onto the component side of the board.
A number of prior-art devices have been used to prevent or minimize the foregoing problems, but each has been found to be deficient in one or more of the areas of effectiveness, damage to the connectors, cost, life or labor required in its use. For example, clip-on devices of various types have been used. Those comprised of one piece of spring metal tend to scratch the gold contacts as they are slipped on and off the edge of the circuit board, and this condition appears to worsen as they are reused over a period of time. Covering the metal with a smooth high temperature material, such as Teflon, solves the scratching problem, but these devices are expensive and have a limited life. Other clip-on devices involving an assembly of hinged parts have been found to be less effective and to require high maintenance due to the entry of solder into the moving parts. Slotted rubber extrusions adapted to slip over the edge of the board have been employed but these are relatively fragile and provide no stiffness to prevent board sagging during the solder operation. Cast rubber and metal devices are reasonably effective but are fragile and difficult to manufacture. A well known method of masking the contacts involves the use of high temperature tape with an adhesive backing which is placed over the contacts. This technique requires considerable time and labor to apply the tape carefully and to remove it after soldering. Moreover, it does not provide the required board stiffness and a dam to prevent solder overflow onto the components.
What is required of the protective device is that it be easily applied to the circuit board assembly, stay in place and be readily removable without at any time scratching the surface of the edge contacts. It must resist solder temperatures and be rugged in construction since it is subjected to handling by heavily gloved hands. It must have reasonable life, cost and labor requirements. Finally, it must provide board stiffness and a dam to prevent solder from flowing over the top of the board. The device of the present invention meets all of the foregoing requirements.